移动设备上的全屏、全 dpi WebGL 画布

Question

有什么方法可以使移动设备上的画布尺寸1比1为设备屏幕真实像素尺寸？

这对于直接从站点支持 Google Cardboard (VR) 应用程序非常重要。 （在这种情况下 dpi 确实很重要）

目前使用视口目标密度dpi 的唯一方法已被弃用，并且不适用于现代浏览器。

Answer 1

最简单的方法是使用 CSS 来决定画布的大小。然后使用

canvas.clientWidth

和

canvas.clientHeight

查找浏览器显示画布的 CSS 像素大小。现在将其乘以

window.devicePixelRatio

即可获取这些 CSS 像素代表的设备像素数，并设置画布的内容/绘图缓冲区大小以匹配。

示例：

1. 制作画布

   <canvas id="c"></canvas>  
   

2. 使用 CSS 设置其大小

   这里我将画布设置为视口（窗口）的大小。

   html, body {
     margin: 0;     /* remove the default margin */
     height: 100%;  /* make the body fill the window */
   }
   canvas {
     width: 100%;    /* make the canvas fill the body */
     height: 100%; 
     display: block; /* make the canvas not cause a scrollbar */
   }
   

3. 查找其显示的大小并匹配其绘图缓冲区大小。

    function resizeToMatchDisplaySize(canvas) {
      var displayWidth  = canvas.clientWidth  * window.devicePixelRatio;
      var displayHeight = canvas.clientHeight * window.devicePixelRatio;
      if (canvas.width !== displayWidth || canvas.height !== displayHeight) {
        canvas.width  = displayWidth;
        canvas.height = displayHeight;
        return true;
      }
      return false;
    }
   

4. 渲染每帧之前调整大小

    function render() {
      // resize before rendering in case of resizing or rotation
      if (resizeToMatchDisplaySize(gl.canvas)) {
        gl.viewport(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight); 
      }
   
   
      // render scene
   
      requestAnimationFrame(render);
    }
    requestAnimationFrame(render);
   

这是一个绘制线条的示例

var gl = document.querySelector("#c").getContext("webgl", { alpha: false });
var programInfo = twgl.createProgramInfo(gl, ['vs', 'fs']);
var ids = [];
for (var i = 0; i < 500; ++i) {
  ids.push(i);
}
var arrays = {
  vertexId: { size:1, data: ids},
};
var bufferInfo = twgl.createBufferInfoFromArrays(gl, arrays);

var uniforms = {
  time: 0,
  numIds: ids.length,
  resolution: [0, 0],
};

function resizeToMatchDisplaySize(canvas) {
  var displayWidth  = canvas.clientWidth  * window.devicePixelRatio;
  var displayHeight = canvas.clientHeight * window.devicePixelRatio;
  if (canvas.width !== displayWidth || canvas.height !== displayHeight) {
    canvas.width  = displayWidth;
    canvas.height = displayHeight;
    return true;
  }
  return false;
}

function render(time) {
  // resize before rendering in case of resizing or rotation
  if (resizeToMatchDisplaySize(gl.canvas)) {
    gl.viewport(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight);
  }
  
  // render scene
  gl.useProgram(programInfo.program);
  uniforms.time = time * 0.001;
  uniforms.resolution[0] = gl.drawingBufferWidth;
  uniforms.resolution[1] = gl.drawingBufferHeight;
  twgl.setBuffersAndAttributes(gl, programInfo, bufferInfo);
  twgl.setUniforms(programInfo, uniforms);
  twgl.drawBufferInfo(gl, gl.LINES, bufferInfo);
  
  requestAnimationFrame(render);
}
requestAnimationFrame(render);

html, body {
  height: 100%;
  margin: 0;
}
canvas {
  width: 100%;
  height: 100%;
  display: block;
}

<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">
<canvas id="c"></canvas>
  <script id="vs" type="notjs">
attribute float vertexId;

varying vec4 v_color;

uniform float numIds;
uniform float time;
uniform vec2 resolution;

#define PI radians(180.0)

vec3 hsv2rgb(vec3 c) {
  c = vec3(c.x, clamp(c.yz, 0.0, 1.0));
  vec4 K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
  vec3 p = abs(fract(c.xxx + K.xyz) * 6.0 - K.www);
  return c.z * mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), c.y);
}


void main() {
  vec4 offsets = vec4(
    sin(time), 
    sin(time * .13) * PI * 2.,
    sin(time * .43) * .5 + 1.,
    cos(time * .17) * .5 + .5);

  vec4 centers = vec4(
    sin(time * .163) * .5,
    cos(time * .267) * .5,
    sin(time * .367) * .5,
    cos(time * .497) * .5);

  vec4 mult = vec4(
    1.,
    (sin(time * .1) * .5 + .5) * 3.,
    0.,
    0.);

  vec2 position = vec2(vertexId / numIds, mod(vertexId, 2.));
  vec2 offset = mix(offsets.xz, offsets.yw, position.y);
  float a = mult.x * position.x * PI * 2.0 + offset.x;//mix(u_offsets.x, u_offsets.y, a_position.y);
  float c = cos(a * mult.y);
  vec2 xy = vec2(
    cos(a),
    sin(a)) * c * offset.y +
    mix(centers.xy, centers.zw, position.y);
  vec2 aspect = vec2(resolution.y / resolution.x, 1);
  gl_Position = vec4(xy * aspect, 0, 1);
  
  float hue = position.x;
  float sat = 1.;
  float val = 1.;
  v_color = vec4(hsv2rgb(vec3(hue, sat, val)), 1);
}
  </script>
  <script id="fs" type="notjs">
precision mediump float;
varying vec4 v_color;
void main() {
  gl_FragColor = v_color;
}
  </script>
  <script src="https://twgljs.org/dist/twgl-full.min.js"></script>

请注意，您已经问了 2 个问题。如何获得原生 1x1 像素以及如何进入全屏。全屏更难。 iOS Safari 不支持全屏 API。 Android 版 Chrome 可以，但它要求您的网站通过 HTTPS 提供服务。

您还应该将其放入您的

<head>

部分

<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">

并根据您的需要将

user-scalable

设置为

yes

或

no